Liquid developers for electrostatic photography

ABSTRACT

A liquid developer for electrostatic photography is prepared by dispersing in a dispersion medium composed essentially of a paraffinic hydrocarbon, an alkylaminoethyl methacrylatecontaining polymer; a carboxyl group-containing copolymer or acrylic or methacrylic acid and an ester thereof; a coloring material; and/or a dihydroabietic ester. Colloidal particles of the developer have favorable electric charging properties, and, after development of a photoconductive material and simultaneously with the drying of the liquid, they firmly adhere to the photo-sensitive layer to give a clear image. Further, the developer, which is a colloidal dispersion system, is stable and does not easily cause precipitation or agglomeration.

United States Patent Kurita et a1.

[54] LIQUID DEVELOPERS FOR ELECTROSTATIC PHOTOGRAPHY [72] Inventors: Takaji Kurita; Masaya Motoki; Kazuhiro Emoto; Katsuo I-Iojo, all of Otokuni-gun,

Kyoto, Japan [73] Assignee: Mitsubishi Paper Mills, Ltd., Tokyo, Japan 22 Filed: July 24, 1969 [21] Appl. No.: 844,598

[30] Foreign Application Priority Data July 27, 1968 Japan ..43/53234 Feb. 14, 1969 Japan ..44/ 131769 [52] US. Cl ..252/62.1, 117/37 LE, 260/336 UA [51] Int. Cl. ..G03g 9/04 [58] Field of Search ..252/62.1; 117/37 LX; 260/861 N [56] References Cited UNITED STATES PATENTS 2,138,763 1 H1938 Grauep ..260/86.1 N

[451 June 20, 1972 Fields et a1 ..260/86.l N Roteman ..1 17/37 LX [5 7] ABSTRACT A liquid developer for electrostatic photography is prepared by dispersing in a dispersion medium composed essentially of a parafiinic hydrocarbon, an alkylaminoethyl methacrylatecontaining polymer; a carboxyl group-containing copolymer or acrylic or methacrylic acid and an ester thereof; a coloring material; and/or a dihydroabietic ester.

Colloidal particles of the developer have favorable electric charging properties, and, after development of a photoconductive material and simultaneously with the drying of the liquid, they firmly adhere to the photo-sensitive layer to give a clear image. Further, the developer, which is a colloidal dispersion system, is stable and does not easily cause precipitation or agglomeration.

9 Claims, No Drawings LIQUID DEVELOPERS FOR ELECTROSTATIC PHOTOGRAPHY This invention relates to a developer for developing electrostatic images in electrostatic photography which is composed of colloidal particles dispersed in an insulating liquid.

In electrostatic photography, an image is formed, in general, as a positively or negatively charged pattern, by action of light or radioactive rays, on a thin layer of a photoconductive insulator and, in order to make said image visible, there is used a charged, fine, colored powder, which is ordinarily called a toner or a developer. in the liquid development method, there is employed a developer which is prepared by dispersing, in the form of a colloid, fine particles of pigment, dye or synthetic resin in a liquid having a high resistivity such as 0. cm or more. In view of the surface chemistry, these fine particles have an electric charge of a definite sign to the liquid. By virtue of said electric charge, the particles adhere to an electrostatic image to carry out the development thereof. In order to be usable as a developer, said particles desirably have a favorable electric charging property and, after the development and simultaneously with the drying of the liquid, firmly adhere to the photoconductive layer. Further, it is necessary that the colloidal dispersion system is stable and does not easily cause precipitation or agglomeration.

In accordance with the present invention explained below, there is provided a developer capable of satisfying such conditions as mentioned above. That is, the present inventors have been able to prepare a developer having excellent adhesiveness and dispersibility by using an amino group-containing polymer and a carboxyl group-containing copolymer of acrylic or methacrylic acid and an ester thereof.

As a dispersion medium employed in the present developer, a common isoparaffinic hydrocarbon is ordinarily used, through the use of a purified normal paraffin is also possible. Of the two synthetic resins employed in the present developer, the amino group-containing polymer includes polymers containing alkylaminoethyl methacrylates, while the carboxyl group-containing copolymer of acrylic or methacrylic acid and an ester thereof includes copolymers which contain long chain alkyl groups and which are soluble in paraffinic hydrocarbons. Examples of preferable polymers containing alkylaminoethyl rnethacrylates are polydialkylaminoethyl methacrylates, copolymers of dialkylaminoethyl methacrylates and styrene, and copolymers of dialkylaminoethyl methacrylates, styrene and alkyl methacrylates. Examples of the carboxyl group-containing copolymers of acrylic or methacrylic acid and esters thereof are copolymers comprising lauryl methacrylate and methacrylic acid in a polymerization molar ratio of from 99 l to 90 l0, copolymers comprising lauryl methacrylate and acrylic acid in a polymerization molar ratio of from 99 l to 90 10, and copolymers comprising stearyl acrylate and acrylic acid. In addition thereto, copolymers containing maleic, crotonic or the like acid may also be used. Alkyl groups in the above-mentioned alkyl methacrylates or acrylates are required to have at least six carbon atoms.

The above-mentioned alkylaminoethyl methacrylate-containing polymers are preferably those which are soft and insoluble in aliphatic hydrocarbon solvents. They are soluble, within a certain limit, in aliphatic hydrocarbon solvent solutions of the aforesaid copolymers of methacrylic or acrylic acid andesters thereof which contain long chain alkyl groups and carboxyl groups. This is considered ascribable to the phenomenon that the amino groups in the alkylaminoethyl methacrylate polymers and the carboxyl groups in the soluble copolymers bond together to solubilize the alkylaminoethyl methacrylate polymers. A solution, in which the polymers have been completely solubilized, is transparent, contains no colloidal particles in appearance, and has no developability when used as it is. However, if the amount of alkylaminoethyl methacrylate polymer is increased to exceed the limit of solubilization, the solution becomes a turbid liquid. Such a liquid contains, dispersed therein, fine colloidal particles of polyaminoethyl methacrylate derivative which have an electric charge to the liquid. Accordingly, when an electrostatic image-bearing photoconductive layer is immersed in said liquid, the colloidal particles of polyalkylaminoethyl methacrylate resin adhere to the electrostatic image to give an image which, when viewed under a specular light, generates a beautiful lustre.

The colloidal resin system obtained in the above manner is not sufficiently stable but agglomerates when allowed to stand for a long period of time. If, however, fine pigment or dye particles have previously been dispersed during the formation of said colloid, the colloidal resin particles grow, using said pigment or dye particles as cores, to form a stable dispersion system, and the colloidal particles have favorable electric charge and come to have excellent properties as a developer for electrostatic images. Further, it has been found that the above-mentioned colloidal system can be made more stable by addition of methyl glycerin, or diethylene-glycol dihydroabietate or a divalent or trivalent salt of dihydroabietic acid.

The aforesaid dye or pigment particles are preferably added in an amount of 0.5 10 g. per cc. of the dispersion medium, and the mixing ratio of the alkylamino-ethyl methacrylate-containing polymer to the copolymer of acrylic or methacrylic acid or an ester thereof is preferably 1/ 10-1 1. Further, the amount of acid in said copolymer is desirably controlled to 10 percent or less.

The following examples illustrate the present invention.

EXAMPLE 1 Phthalocyanine Blue 0.3 g. Dimethylaminoethyl methacrylate polymer 0.5 g. Copolymer of methacrylic acid and lauryl methacrylate (molar ratio 6 94) 0.8 g. Xylene 2 cc.

A mixture of the above-mentioned compounds is thoroughly dispersed by means of an ultrasonic dispersing apparatus, and an isoparaffinic hydrocarbon solvent (e. g. lsopar H produced by Esso Standard Oil Co.) is gradually added to make the total amount 10 cc. The thus prepared liquid contains colloidal particles of the dimethylaminoethyl methacrylate resin polymer which have particles of Phthalocyanine Blue as cores, and forms a stable dispersion system by the dispersing action of the methacrylic acid-lauryl methacrylate copolymer. 1 cc. of this dispersion is diluted with 100 cc. of an isoparafiinic hydrocarbon solvent (e.g. lsopar H) to obtain a developer for electrostatic photography. In this liquid, the particles have a positive charge, and when the liquid is used to develop a latent electrostatic image, for example, on a zinc oxide electrophotographic paper known as Electrofax, there is obtained a beautiful blue image. Simultaneously with the drying of the liquid, the colloidal particles, which have formed the image, firmly adhere (fix) onto the surface of the photoconductive layer and are brought into such a state that they do not easily come off by rubbing or the like. This is considered ascribable to the fact that the dimethylaminoethyl methacrylate polymer gives a considerable adhesiveness to the developed image. It is an advantage of this procedure that a developer having such an excellent adhesiveness can be prepared.

EXAMPLE 2 Oil Black 0.2 g. Carbon black 0.5 g. Diethylarninoethyl methacrylate polymer 0.3 g. Copolymer of acrylic acid and stearyl methacrylate (Molar ratio 8 z 92) 0.6 g.

Toluene 2.0 cc.

A mixture of the above-mentioned compounds is treated in the same manner as in Example 1 to obtain a developer. The developer gives a clear pure black image and is excellent in fixing property. When this developer is incorporated with 5 g. of methyl dihydroabietate, the colloid is improved in stability.

EXAMPLE 3 Oil Blue 80 0.3 g. Microlith Black CT 0.5 g. Copolymer of diethylaminoethyl methacrylate, styrene and lauryl methacrylate (Molar ratio 3 2) 0.3 g. Copolymer of methacrylic acid and ethylhexyl methacrylate (Molar ratio 4 96) 0.6 g. Toluene 2 cc. lsoparaffinic hydrocarbon 3 cc.

In the above, Microlith Black CT is a black pigment produced by Ciba Products Ltd., Switzerland and as the isoparaffinic hydrocarbon, there is used, for example, Shellsol 71 produced by Shell Oil Co., England or the like.

. A mixture of the above-mentioned compounds is treated in the same manner as in Example 1 to obtain a developer. All

EXAMPLE 4 Carbon black 0.5 g. Oil Black 0.2 g. Phthalocyanine Blue 0.1 g. Gilsonite 1.0 g. Copolymer of dimethylaminoethyl methacrylate and styrene (Molar ratio 1 2) 0.4 g. Copolymer of acrylic acid and lauryl methacrylate (Molar ratio 3 97) 0.4 g. Toluene 2 cc. lsoparafi'rnic hydrocarbon 3 cc.

A mixture of the above-mentioned compounds is thoroughly dispersed by means of an ultrasonic dispersing apparatus, and is gradually diluted with an isoparaffinic hydrocarbon (e.g. Shellsol 71) to make the total amount 25 cc. During the course of said dilution, colloidal resin particles having the pigment particles as cores are formed. 1 cc. of the thus prepared liquid is dispersed in 100 cc. of Shellsol 7 l and the dispersion is used as a developer. The colloidal particles in the developer have been negatively charged, and when used to develop an electrostatic photographic paper with negative original, the developer gives a clear positive image excellent in fixing property, though the image is somewhat low in optical density. Substantially the same results as above can be obtained even when the copolymer of acrylic acid and lauryl methacrylate (molar ratio 3 97) is replaced by a copolymer of methacrylic acid and lauryl methacrylate. When the developer is incorporated with methyl dihydroabietate, the colloid is increased in stability.

EXAMPLE 5 Carbon black 0.5 g. Oil Black 0.3 g. Rosin-modified maleic acid resin 1.2 g. Low molecular weight polystyrene 2.8 g. Copal 1.0 g.

A mixture of the above-mentioned compounds is heated and melted in an oil bath at 180 C., and is thoroughly stirred to a homogeneous mixture. After being allowed to cool, the mixture is ground in a mortar. To the resulting powder are added the following compounds:

Dimethylaminoethyl methacrylate polymer 1.2 g. Copolymer of methacrylic acid and lauryl methacrylate (molar ratio 6 94) 2.0 g. lsoparalfinic hydrocarbon (e.g. Shellsol 71) 2.0 g.

Subsequently, the mixture is thoroughly stirred to homogeneity and is then gradually charged, under vigorous stirring, with an isoparafiinic hydrocarbon to make the total amount 30 cc. Thereafter, the mixture is dispersed by means of an ultrasonic dispersing apparatus. 1 cc. of the thus prepared liquid is diluted with cc. of an isoparaffinic hydrocarbon to obtain a developer. in this liquid, the pigment particles have not only been enveloped with the aforesaid thermoplastic resin but also have been covered thereon with the dimethylaminoethyl methacrylate polymer and the methacrylic acid-containing copolymer, and hence have favorable electric charging property and dispersibility. In this developer, the particles have a positive charge, and when the developer is used to develop a zinc oxide electrophotographic paper, there is obtained a clear positive image high in optical density.

EXAMPLE 6 5O Toluene solution of copolymer of diethylaminoethyl methacrylate, styrene and lauryl methacrylate A mixture of the above-mentioned compounds is dispersed and is then charged with the following compounds:

Methyl dihydroabietate [0.0 g. Aluminum dihydroabietate 20 mg. Shellsol 71 80.0 g.

The mixture is dispersed by means of an ultrasonic dispersing apparatus and is then diluted to 300 times to obtain a developer. This developer gives a clear positive image high in optical density and, simultaneously with the drying of the liquid, the image is fixed without heating.

Advantages common to the developers prepared according to such processes as mentioned above are such that the colloidal particles are excellent in electric charging property and dispersibility to give clear images high in contrast, and developed images show excellent fixing properties without any particular heating. Further, a colloidal system composed only of a resin can be prepared, and when said resin, e.g., a dimethylaminoethyl methacrylate-containing copolymer, has previously been dyed with a coloring material, it is also possible to obtain a colored developed image.

As has also been described in the above examples, the addition of methyl dihydroabietate or a calcium, manganese, barium, zinc or aluminum salt of dihydroabietic acid is effective for the enhancement in stability of the colloid.

What is claimed is:

l. A liquid developer for electrostatic photography consist ing of a dispersion medium composed essentially of a paraffinic hydrocarbon having a resistivity of at least 10 0. cm, and the following constituents dispersed in said medium (i) an alkylaminoethyl methacrylate-containing polymer whose alkyl group contains one to two carbon atoms and which is selected from the group consisting of polydialkylaminoethyl methacrylates, copolymers of dialkylaminoethyl methacrylates and styrene, and copolymers of dialkylaminoethyl methacrylates, styrene and alkylmethacrylates having an alkyl group containing at least six carbon atoms, (ii) a carboxyl group-containing copolymer of acrylic or methacrylic acid and an alkylacrylate or alkylmethacrylate whose alkyl group contains at least six carbon atoms, the polymerization molar ratio of the two components being between 1 99, and 10 90, (iii) 0.5 to 10 g per 100 cc of dispersion medium of particles of a pigment or dye, or mixture thereof capable of forming cores for colloidal particles of polyalkylaminoethyl methacrylate resins which are formed to form a stable dispersion system; and, (iv) as a colloid stabilizer an operative amount of dihydroabietic ester or a salt of a dior trivalent metal of dihydroabietic acid.

2. A liquid developer according to claim 1, wherein the polydialkylaminoethyl methacrylates are polydimethylaminoethyl methacrylates or polydiethylaminoethyl methacrylates.

3. A liquid developer according to claim 1, wherein the alkylaminoethyl methacrylate-containing polymer is one member selected from the group consisting of polydialkylaminoethyl methacrylates, copolymers of 33 percent dialkylaminoethyl methacrylates and 67 percent styrene, and copolymers of 30 percent dialkylaminoethyl methacrylates, 50 percent styrene and 20 percent alkyl methacrylates.

4. A liquid developer according to claim 1 wherein the carboxyl group containing copolymer is a copolymer of 6 percent methacrylic acid and 94 percent lauryl methacrylate, a copolymer of 3 percent acrylic acid and 97 percent lauryl methacrylate, a copolymer of 8 percent acrylic acid and 92 percent stearyl acrylate, or a copolymer of 4 percent methacrylic acid and 96 percent ethylhexyl methacrylate.

5. A liquid developer according to claim 1, wherein the pigment is carbon black or phthalocyanine blue and the dye is oil black or oil blue.

6. A liquid developer according to claim 1, wherein the dihydroabietic ester is methyl glycerin dihydroabietate, or diethylene glycol dihydroabietate.

7. A liquid developer according to claim 1, wherein the dior trivalent metal salt is selected from the group consisting of Ca, Mn, Ba, Zn and Al salts of dihydroabietic acid.

8. A liquid developer according to claim 1, wherein the ratio of the alkylaminoethyl methacrylate-containing polymer to the carboxyl group containing copolymer is between 1 l0 and 1 l.

9. A liquid developer according to claim 1, wherein the amount of acid in the carboxyl group containing copolymer is less than 10 percent.

Patent No. 3,671,646 Dated June 20, 1972 Inventor(s) Takaji Kurita, et. a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet [30] "Febe 14, 1969", should read Feb. 24, 1969 also "44/131769" should read 44/13176 1 Signed andsealed this ISth day of May 1973.

(SEAL) Attest: I

EDWARD M.FLEICHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-105O (10-69) USCOMM-DC scams9 US. GOVERNMENT PRINTING OFFICE: 1969 0-366-334, 

2. A liquid developer according to claim 1, wherein the polydialkylaminoethyl methacrylates are polydimethylaminoethyl methacrylates or polydiethylaminoethyl methacrylates.
 3. A liquid developer according to claim 1, wherein the alkylaminoethyl methacrylate-containing polymer is one member selected from the group consisting of polydialkylaminoethyl methacrylates, copolymers of 33 percent dialkylaminoethyl methacrylates and 67 percent styrene, and copolymers of 30 percent dialkylaminoethyl methacrylates, 50 percent styrene and 20 percent alkyl methacrylates.
 4. A liquid developer according to claim 1 wherein the carboxyl group - containing copolymer is a copolymer of 6 percent methacrylic acid and 94 percent lauryl methacrylate, a copolymer of 3 percent acrylic acid and 97 percent lauryl methacrylate, a copolymer of 8 percent acrylic acid and 92 percent stearyl acrylate, or a copolymer of 4 percent methacrylic acid and 96 percent ethylhexyl methacrylate.
 5. A liquid developer according to claim 1, wherein the pigment is carbon black or phthalocyanine blue and the dye is oil black or oil blue.
 6. A liquid developer according to claim 1, wherein the dihydroabietic ester is methyl glycerin dihydroabietate, or diethylene glycol dihydroabietate.
 7. A liquid developer according to claim 1, wherein the di- or trivalent metal salt is selected from the group consisting of Ca, Mn, Ba, Zn and Al salts of dihydroabietic acid.
 8. A liquid developer according to claim 1, wherein the ratio of the alkylaminoethyl methacrylate-containing polymer to the carboxyl group - containing copolymer is between 1/10 and 1 :
 1. 9. A liquid developer according to claim 1, wherein the amount of acid in the carboxyl - group containing copolymer is less than 10 percent. 